The present invention relates to the control of an image density in an image recording apparatus such as a copying machine or the like.
Image recording apparatus such as copying machines which employ general photosensitive materials control the density of output images by controlling the intensity of light emitted from the light source. When the intensity of light emitted from the light source is varied due to fluctuation in the voltage of a power supply, it is general to measure the light intensity with a light intensity sensor and control the light source to emit light at a proper intensity level based on the measured light intensity.
A generally used photosensitive material such as PPC or the like is highly sensitive and can sufficiently be exposed to light at a relatively low intensity level. Therefore, it is easy to increase the intensity of light from the light source for controlling the light intensity to compensate for fluctuations in the power supply voltage or to lower the density of images to be formed.
There have also been employed less sensitive photosensitive materials such as a microcapsule-coated sheet and a color developer sheet. These less sensitive photosensitive materials are required to be exposed to light having a very high intensity. Since the intensity of light emitted from the light source is limited by the limited capacities of the lamp of the light source and the power supply coupled to the light source, required light intensities may not be obtained when it is desired to increase the light intensity to lower the density of images to be generated by the image recording apparatus or when the voltage applied by the power supply is lowered.
Heretofore, in the event of a light intensity shortage, an error indication representing such a light intensity shortage is given and then the image recording apparatus is shut off in order to prevent defective images from being formed by the image recording apparatus.